Contributions to the numerical modeling of concrete structures cracking with creep and estimation of the permeability

The industrial context of this research work is to study the durability of the internal barriers of nuclear power plants. This paper is divided in two parts, the first part is relative to the crack-damage state and the second part to the creep consequences on the rupture properties of concrete. In the first part, the analysis of the experimental results, (carried out on a compression cylinder on which the radial permeability has been measured), shows that the permeability decreases until a deformation of half of those at the force peak, by re-closure of the preexisting microcracks in the material; then the permeability strongly increases until after the force peak by initiation, connexion and opening of the crack, and at last it increases less rapidly until the rupture because only the opening of the macro-cracks increases. In order to simulate these phenomena, two original methods are presented, in post-treatment phase, for estimating the leaks from a mechanical computing based on finite element methods. With the first method, it is possible to measure the permeability from the damage field and from a relation between the permeability and the damage which bind the Poiseuille law to an empirical law established for weak damages. The second method is on the deformations field from which the position and opening of the crack are calculated. The Poiseuille relation is then applied along the crack to estimate the leaks rates. The relation between the concrete creep and its mechanical characteristics is analyzed in the second part. In particular, are studied the creep consequences on the long term mechanical properties. After having given the experimental results which show essentially an embrittlement of the material after creep, a qualitative analysis by the bifurcations study is proposed, and then by a discrete numerical method to find again the same influence of the visco-elasticity on the rupture embrittlement experimentally observed. At last, the first results of the quantitative analysis by a finite element method using an original coupled model are presented. (O.M.)